JP6697396B2 - Target assembly for irradiating molybdenum with a particle beam and manufacturing method thereof - Google Patents

Description

  The present disclosure relates to producing technetium-99m and molybdenum-99 from molybdenum-100 using a particle accelerator exemplified by a cyclotron. In particular, the present disclosure relates to target systems for producing technetium and molybdenum radioisotopes by irradiating molybdenum with charged particles.

  Technetium-99m (Tc-99m) is a radioisotope widely used in nuclear medicine diagnostic techniques. Technetium-99m emits 140 keV gamma rays and decays with a half-life of about 6 hours. In a typical diagnostic procedure, the appropriate tracer molecule is labeled with Tc-99m, the radiopharmaceutical is injected into the body of the patient, and imaged with a radiograph.

Currently, Tc-99m is supplied in the form of molybdenum-99 / technetium-99m generator. The parent isotope molybdenum-99 (Mo-99) is produced in a nuclear reactor. Mo-99 has a half-life of 66 hours, which allows its worldwide distribution to healthcare facilities. The Mo-99 / Tc-99m generator uses column chromatography to separate Tc-99m from Mo-99. Mo-99 is loaded onto an acidic alumina column in the form of molybdate: MoO ₄ ²⁻ . As the Mo-99 decays, pertechnetate: TcO ₄ ⁻ is produced and can be selectively eluted with sodium chloride from the generator column as sodium pertechnetate. The solution containing sodium pertechnetate is then typically added to a radiochemical "kit" to produce an organ-specific radiopharmaceutical.

  Some reactors producing Mo-99 in the world are nearing their end of life. Some of the major facilities, such as the Chalk River Laboratories in Ontario, Canada, and the Petertern Reactor in the Netherlands, have substantial outages, which means the global availability of Mo-99 for medical applications. Caused a shortage in. There remains great concern regarding the reliable and long-term supply of Mo-99.

  For research purposes only, small amounts of radioisotopes can be produced by interacting with a Mo-100 target using a beam of accelerated particles generated by an accelerator, which causes nuclear transmutation. , Mo-100 changes to Mo-99. However, the scalability of such systems is limited by a number of problems. For example, thermal energy is generated at the same time that the target material absorbs the accelerated particles and must be dissipated to avoid damage to the target system and system components. In some small scale systems, water cooling can be used to remove the heat load from the target, thus building the target assembly containing the target material from a material with high thermal conductivity to allow bombardment with accelerated particles. It can maximize heat dissipation inside. Silver and copper can be used to make small scale target assemblies. However, when exposed to elevated temperatures for extended periods of time, both silver and copper anneal at low temperatures of 100 ° C. Furthermore, these compounds are annealed rapidly and completely at temperatures above 500 ° C. Such annealing renders the target assembly and the targets contained in the assembly intolerant of the mechanical stress of water cooling. In addition, the target material itself may deform due to thermal stress during bombardment with accelerated particles.

  Exemplary embodiments of the present disclosure produce technetium and molybdenum radioisotopes from molybdenum metal, such as Tc-99m and Mo-99, from molybdenum-100 (Mo-100) by irradiation of particles from accelerators such as cyclotons. For the target system to do.

  The drawings described herein are for purposes of illustrating selected embodiments only and are not intended to limit the scope of the present disclosure.

FIG. 6 is a perspective view of three components of an exemplary Mo-100 target assembly disclosed herein. It is a perspective view which shows what assembled two of the components shown in FIG. 2 is a perspective view of the three components shown in FIG. 1 assembled with a tantalum weight that holds the components in place. FIG. FIG. 7 is a side view of an exemplary Mo-100 target assembly assembled. FIG. 7 is a top view of an exemplary Mo-100 target assembly assembled. FIG. 6 is a perspective view of an exemplary Mo-100 target assembly assembled.

  Some exemplary embodiments of the present disclosure relate to a target assembly including a target holder for housing a Mo-100 target for bombardment with accelerated particles and a bombarded target engaged with the target holder.

  Some example embodiments relate to methods of assembling and preparing a target assembly for bombardment with accelerated particles.

  If the process requires elevated temperatures, it is generally necessary to prepare the metal molybdenum target in an inert atmosphere because molybdenum reacts rapidly with oxygen when heated to temperatures above 400 ° C. Is. Instead of an inert atmosphere, a reducing gas mixture exemplified by hydrogen in argon can be applied to protect molybdenum from oxidation and reduce the molybdenum oxide contained in the target material to molybdenum metal.

  Joining refractory metals such as molybdenum to other materials typically involves complex multi-step processes. Soldering or brazing of such metals usually involves extensive pretreatment of the surfaces to be joined (degreasing, sanding, chemical etching, precoating with a suitable metal) and a strong, possibly toxic flux material. Need to apply. Mo-100 soldering or brazing can only be accomplished under oxygen exclusion.

Example embodiments of the present disclosure relate to a process for making a target system consisting of a metallic Mo-100 body that is brazed in a furnace to a backing material of high thermal conductivity and high mechanical strength. These steps are generally
(1) Pressing a certain amount of molybdenum powder using a mechanical device to form a compressed Mo-100 plate having a desired thickness and size,
(2) Sintering the compressed Mo-100 plate in an inert or reducing atmosphere for about 2 to about 20 hours at a temperature in the range of about 1300 to about 2100 ° C.
(3) GLIDCOP metal matrix composite alloy (GLIDCOP is North American Hoganas, Hallsopple, PA, USA) at a temperature in the range of about 500 to about 1000 ° C. in a furnace in a vacuum or in an inert or reducing atmosphere. Sintered Mo-100 plate and backing material with a high mechanical strength, high thermal conductivity and high ductility bond to a backing formed from a dispersion strengthened copper composite material exemplified by High Alloys LLC). And brazing with a brazing filler suitable for forming between.

  An exemplary embodiment disclosed herein illustrates a molybdenum target in a small medical cyclotron, such as the cyclotron illustrated by GE PETTRACE (PETTRACE is a registered trademark of General Electric Company Corp., Schenectady, NY, USA). The production of a solid molybdenum target for the production of Tc-99m by irradiating a beam current of up to 130 μA with 16.5 MeV protons is described. A suitable target assembly for use with the PETTRACE® cyclotron may comprise an exemplary target holder having an outer diameter of about 30 mm and a thickness of about 1.3 mm. The exemplary target holder is provided with a recess having a diameter of about 20 mm and a depth of about 0.7 mm. A sintered Mo-100 disc having a diameter of about 18.5 to about 19.5 mm and a thickness of about 0.6 mm is housed in the recess of this exemplary target holder and brazed to securely engage the target holder.

  The first step in an exemplary method for manufacturing an exemplary target assembly containing a sintered Mo-100 target involves making a Mo-100 target disk. A selected amount of commercially available Mo-100 powder is transferred to a cylindrical disk form using a cylindrical tool and die set. The Mo-100 powder is then pressed onto a compression molded disk by applying pressure with a hydraulic press to a cylindrical mold / die set containing the Mo-100 powder. The compression molded Mo-100 disc is removed from the die and transferred to a ceramic container for further processing.

  For example, a 20 mm diameter compression molded Mo-100 disk can be prepared using a hardened steel cylindrical mold / die set, which (1) receives and positions 20 mm diameter spacer pellets. A base configured to receive and releasably engage a cylindrical sleeve having a recess for receiving and having a 20 mm diameter bore; (2) a cylindrical sleeve; and (3) at least two 20 mm diameter sleeves. And spacer pellets. A suitable cylindrical mold / die set is exemplified by the Access International (Livingston, NJ, USA) ID 20 mm ID dry press die set. Spread a small amount of Vaseline lubricant on the top, bottom and sides of the two spacer pellets. One spacer pellet is placed in a recess in the base and then a cylindrical sleeve is overlaid on the spacer pellet and then engaged with the base. Next, the appropriate amount of pre-weighed concentrated Mo-100 powder is poured into the cavity in the cylindrical sleeve and packed into place. A suitable amount of Mo-100 powder for preparing a 20 mm diameter Mo-100 disk is about 1.6 g. Range of 0.3-3.0g, for example 0.3g, 0.5g, 0.75g, 1.0g, 1.25g, 1.5g, 1.75g, 2.0g, 2.25g, 2.5g Amounts of 2.75g, 3g are also suitable. The second spacer pellet is then inserted into the cavity in the cylindrical sleeve until it reaches the top of the Mo-100 powder. Then, a piston, which may be prepared with a mold / die set, is inserted into the cavity of the sleeve, engaged with the top of the second spacer pellet, and then manually applied to the piston to apply Mo-100 powder. Is sandwiched between two spacer pellets. Next, the assembled cylindrical mold / die set is transferred to a pellet press, a hydraulic press, a mechanical press or the like. A suitable pellet press is exemplified by the 40 ton laboratory pellet press equipped with a hydraulic pump available from Access International. After mounting the assembled cylindrical mold / die set to the pellet press, the selected pressure is applied to the mold / die set for about 30 seconds. A suitable pressure is about 13608 kg (30000 lbs). In the range of about 907 kg (2000 lbs) to about 45359 kg (100000 lbs), for example, about 907 kg (2000 lbs), about 2268 kg (5000 lbs), about 4536 kg (10000 lbs), about 6804 kg (15000 lbs), about 9072 kg (20000 lbs), about 11340 kg (25000 lbs). , About 13608 kg (30000 lbs), about 15876 kg (35000 lbs), about 18144 kg (40000 lbs), about 20412 kg (45000 lbs), about 22680 kg (50000 lbs), about 29484 kg (65000 lbs), about 27216 kg (60000 lbs), about 2948 kg, about 2948 kg Pressures of 31751 kg (70000 lbs), about 34019 kg (75000 lbs), about 36287 kg (80000 lbs), about 38555 kg (85000 lbs), about 40823 kg (90000 lbs), about 430991 (95000 lbs), about 45359 kg (100000 lbs) are also suitable. After releasing the pressure, the cylindrical mold / die set is removed from the pellet press, the mold / die set is disassembled and the compressed Mo-100 disc is removed into the container.

  The second step of the exemplary method involves sintering a compressed Mo-100 disk in a furnace under a hydrogen / argon atmosphere (eg, 2% / 98% mixture) at a temperature of about 1700 ° C. for 5 hours. To do. For example, the compressed Mo-100 disks made in Step 1 of the exemplary process can be placed in an alumina boat with a flat bottom. Alumina pieces were placed as weights on each compressed Mo-100 disk in an alumina boat, then the alumina boat was placed in a furnace, and then a 2% / 98% hydrogen / argon gas mixture stream with a pressure of about 2 PSI and a flow rate of about 2 L / Start in minutes. Then the temperature is increased from ambient temperature, eg 22 ° C. to 1300 ° C., at 5 ° C./min. Then the temperature is increased from 1300 ° C to 1700 ° C at 2 ° C / min. The furnace is then maintained at 1700 ° C for 5 hours, after which it is cooled from 1700 ° C to 1300 ° C at 2 ° C / min and then to ambient temperature at 5 ° C / min. The cooled sintered Mo-100 disc is then evaluated for bombardment compatibility with accelerated particles. Only the sintered Mo-100 discs that are flat and show no signs of cracking are selected for the third step of this exemplary method.

  The third step of this exemplary method involves preparing the exemplary target assembly. The target holder 20 (FIGS. 1 and 2) is made from a dispersion strengthened copper composite backing exemplified by GLIDCOP® AL-15 with recesses large enough to fit a sintered plate. A suitable size for a target holder for PETTRACE® cyclotron (eg, member 20 of FIGS. 1 and 2) is an outer diameter of 30 mm, a thickness of about 1.3 mm, a diameter of about 20 mm and a depth of about 0.7 mm. It has a recess. The recesses of the target holder are roughened, for example with very fine emery abrasive paper or steel wool, after which the target holder is washed with a cleaning liquid, dried and then placed in methanol and sonicated for about 5 minutes, then To dry. Next, a suitable piece of brazing material 30 having a diameter of approximately 12 mm is placed in the recess of the target holder 20. A suitable braze material is a silver-copper-phosphorus braze material exemplified by SIL-FOS (SIL-FOS is a registered trademark of Handy & Harman Corp. of White Plains, NY, USA). The sintered Mo-100 disc is then placed on top of the braze material, and then the weight 50 (FIG. 3), exemplified by tantalum pellets, is placed on the sintered Mo-100 disc so that the stacked components Prevents movement during the brazing process. The target assembly is heated in a brazing furnace under an argon / hydrogen atmosphere (eg 98%: 2%) to about 750 ° C., maintained at this temperature for 1 hour, then cooled to room temperature.

  It should be noted that the selection of the proper braze material is especially important for successful bonding of the sintered Mo-100 disc to the GLIDCOP® backing material. For example, the product SIL-FOS® sold under the tradename Mattiphos (Johnson Matthey Ltd. of Brampton, Ontario, Canada) in the United States has a rough composition of Ag: 2-18%, Cu: 75-92. %, P: 5 to 7.25% silver-copper-phosphorus material group, which are mainly used for brazing copper and certain copper alloys. SIL-FOS® is commercially available as a rod, strip, wire or foil. SIL-FOS® melts in the range of about 644 to about 800 ° C. and has a pour point of about 700 ° C. The SIL-FOS® brazed joint is highly ductile. When applied to pure copper, phosphorus provides a self-fluxing capability. While brass, bronze and other copper alloys require a separate flux, GLIDCOP® can be brazed with SIL-FOS® alone, thus eliminating the post braze cleaning procedure. SIL-FOS® type brazes were initially developed for copper brazing to copper but have been found to bond to some refractory metals such as molybdenum. The GLIDCOP® brazed molybdenum body may be present as a foil, plate, pellet, compact, sintered or other free standing structure.

  The above process results in an exemplary Mo-100 target system 10 (FIGS. 4, 5, 6) for irradiating the Mo-100 with a high power particle beam, eg, protons from a cyclotron. This exemplary Mo-100 target system 10 includes (i) a backing material 20 that includes a dispersion-strengthened copper composite, (ii) a self-supporting sintered Mo-100 target material 40, and (iii) a backing material 20. Brazing material 30 sandwiched between and engaging Mo-100 target material 40.

  The choice of dispersion strengthened copper composite as the backing material has several advantages over other materials with high thermal conductivity.

  The brazing process described above ensures that the sintered molybdenum plate is bonded to the GLIDCOP® backing. SIL-FOS® provides a uniform, mechanically rigid yet ductile interface between the two components of the assembly. This ductility of the brazed joint plays an important role with respect to its durability under irradiation conditions. During bombardment with high-energy protons, most of the incident beam is absorbed by molybdenum, which significantly increases the temperature of the molybdenum plate. The coefficients of thermal expansion of molybdenum (4.8 μm / m · K) and GLIDCOP® (16.6 μm / m · K) differ greatly. The thermal stress effect between the beam-heated molybdenum and the cooled GLIDCOP® backing is mitigated by the ductile SIL-FOS® boundary layer, which impairs the attachment of the molybdenum plate to the backing. Without contributing to the mechanical stability of the assembly.

Although exemplary embodiments disclosed herein have been described in detail in the context of use in a PETTRACE® cyclotron, one of ordinary skill in the art will recognize that the target holders and compressed Mo-100 disclosed herein. It will be appreciated that by varying the dimensions of the disc, a target holder and compressed Mo-100 disc suitable for use in other devices that generate accelerated particles can be made.
Preferred embodiments of the present invention are as follows.
[1] Sintered molybdenum-100 disc,
A target holder provided with a recess having a flat surface for receiving the sintered molybdenum-100 disc;
An intermediate layer between the disc and the holder comprising a sintered molybdenum-100 disc and a braze alloy that engages the flat surface of the recess of the target holder;
And a molybdenum-100 target assembly.
[2] The molybdenum-100 target assembly according to [1], wherein the target holder contains a dispersion strengthened copper composite material.
[3] The molybdenum-100 target assembly according to the above [1], wherein the brazing alloy contains copper and phosphorus.
[4] A method for producing a molybdenum-100 target assembly, comprising the steps of:
Preparing a compressed molybdenum-100 disc,
Sintering the compressed molybdenum-100 disc,
Brazing the sintered molybdenum-100 disc to the recess provided in the target holder;
Including the method.
[5] The step of preparing the compressed molybdenum-100 disk comprises
Placing a selected amount of molybdenum-100 powder into a cylindrical mold / die set,
Applying a selected pressure to the cylindrical mold / die set for at least 30 seconds,
The method according to [4] above.
[6] The method according to [5] above, wherein the selected amount of the molybdenum-100 powder is selected from the range of 0.3 to 3 g.
[7] The method according to [5] above, wherein the selected amount of the molybdenum-100 powder is 1.6 g.
[8] The method according to [5] above, wherein the selected pressure is selected from the range of about 907 kg (2000 lbs) to about 45359 kg (100000 lbs).
[9] The method according to [5] above, wherein the selected pressure is about 13608 kg (30000 lbs).
[10] The step of sintering the compressed molybdenum-100 disk comprises:
Increasing the temperature from ambient temperature to 1300 ° C. at a rate of 5 ° C./min,
Increasing the temperature from 1300 ° C to 1700 ° C at a rate of 2 ° C / min,
Maintaining the temperature at 1700 ° C. for 5 hours,
Lowering the temperature from 1700 ° C to 1300 ° C at a rate of 2 ° C / min, and
Reducing the temperature from 1300 ° C to ambient temperature at a rate of 5 ° C,
The method according to [4] above.

Claims (9)

Sintered molybdenum-100 disc,
A copper target holder provided with a recess having a flat surface for receiving the sintered molybdenum-100 disc;
An intermediate layer between the disk and the holder comprising a sintered molybdenum-100 disk and a brazing alloy that engages a flat surface of a recess of the target holder , the brazing alloy being copper and An intermediate layer containing phosphorus ,
And a molybdenum-100 target assembly. The molybdenum-100 target assembly of claim 1, wherein the copper target holder comprises a dispersion strengthened copper composite. A method for making the molybdenum-100 target assembly of claim 1 , comprising the steps of:
Placing a selected amount of molybdenum-100 powder into a cylindrical mold / die set and applying circular pressure to the molybdenum-100 powder by applying pressure using the cylindrical mold / die set. Preparing a compressed molybdenum-100 disc by manufacturing the disc ,
Manufacturing a sintered molybdenum-100 disc by sintering the circular compressed molybdenum-100 disc at 1700 ° C. for 5 hours ,
Brazing the sintered molybdenum-100 disc to a recess provided in a copper target holder using a brazing alloy containing copper and phosphorus ;
Including the method. Preparing the compressed molybdenum-100 disc comprises:
Applying a selected pressure to the cylindrical mold / die set for at least 30 seconds,
The method of claim 3 , comprising: The method of claim 4 , wherein the selected amount of molybdenum-100 powder is selected from the range of 0.3-3 g. The method of claim 4 , wherein the selected amount of molybdenum-100 powder is 1.6 g. The method of claim 4 , wherein the selected pressure is selected from the range of 13790 kPa to 689476 kPa (2000 PSI to 100000 PSI) . The method of claim 4 , wherein the selected pressure is 206843 kPa (30000 PSI) . Sintering the compressed molybdenum-100 disc comprises:
Increasing the temperature from ambient temperature to 1300 ° C. at a rate of 5 ° C./min,
Increasing the temperature from 1300 ° C to 1700 ° C at a rate of 2 ° C / min,
Maintaining the temperature at 1700 ° C. for 5 hours,
Reducing the temperature from 1700 ° C to 1300 ° C at a rate of 2 ° C / min, and reducing the temperature from 1300 ° C to ambient temperature at a rate of 5 ° C.
The method of claim 3 , comprising:

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